Hitherto various methods for manufacturing such a material are known, including for example the so-called Bretonstone technology used to manufacture slabs.
These slabs are manufactured using a special technology which involves the preparation of a starting mix comprising a stone and/or stone-like material and a binder, together with any additives.
Generally the binder may be of an inorganic nature, such as cement, or a synthetic resin which can be hardened by means of heat and/or a catalyst.
The starting mix is normally spread over a temporary support which may be a conveyor belt or a tray-like mould.
As is known, natural stone materials (such as marble and granite, to name the most common types) normally have irregular veining, mainly with a colour which contrasts or in any case is different from the basic colour of stone.
In the Bretonstone method hitherto a colouring substance is added after the mix has been deposited on the temporary support.
Said substance is distributed on the surface of the mix in an irregular manner. Then the mix is treated using a spiking apparatus so as to ensure that the colouring agent penetrates inside the mix.
This stage is preceded by a step involving vacuum vibrocompression of the mix. During this step the mix is subject for a given period of time and at a given vacuum value to the action of a press, while a vibratory movement at a predetermined frequency is imparted to the press ram.
The rough-formed slab thus obtained then undergoes a hardening step which depends on the type of binder used.
However, this method is unable to ensure veining throughout the thickness of the slab and is therefore suitable for applications where the edge (or thickness of the article) is not visible.
In fact the action of the spiking apparatus on the mix, following distribution of the colouring agent, is able to achieve the veining effect only over a depth of a few millimeters from the surface, equal to no more than half the thickness of the finished slab.
Alternatively, it is possible to envisage the use of a weighing distributor of the type described in the international patent application WO-A-2004/039547.
According to this production method the starting mix, before being loaded inside a metering device, is subject to the action of devices which apply liquid or powder colouring pigments onto its surface.
The mix comprising the colouring agent is conveyed to the distributor and reaches it by means of a free-falling action so that it undergoes further mixing which, on the one hand, ensures shortening of the veining and, on the other hand, diffusion of the pigment within the mass of the mix which is therefore at least partly coloured en masse.
Another type of technology which is known is Lapitech technology, a term which is understood as referring in general to the technology, the associated method and the resultant slabs. Lapitech technology is used for the manufacture of slabs similar to ceramic articles intended for the internal and external cladding of buildings.
In this case also a starting mix is prepared using a granulated stone, stone-like or ceramic material, preferably in the form of sand of suitable dimensions. The granulated product is mixed with the components which are normally used for the manufacture of ceramic materials, usually in powdery form and consisting mainly of kaolin or clay. A binder, for example sodium silicate in aqueous form or silicasol is then added to the mixture so as to make the mixture moist.
The mix is then extended over a temporary support with a given thickness and then undergoes a vibrocompression step, resulting in a rough-formed slab. Subsequently the rough-formed slab thus obtained undergoes drying in order to remove the water and then firing in an oven at a temperature of about 1200° C.
This technology, as regards the veining effect obtained, is also subject to limitations and drawbacks similar to those mentioned in connection with Bretonstone technology.
The industrial patent application WO-A-2009/010406 describes a method and apparatus for manufacturing slabs with a veined effect.
The procedure and method described are applicable both to Bretonstone technology and to Lapitech technology and the apparatus used is substantially that described in the international patent application No. WO-A-2006/045728.
In the application WO-A-2009/010406 the method is substantially the same as that described above except for a step involving the non-uniform distribution of the colouring agent on the surface of the mix. The distribution of the colouring agent is performed by means of at least one dispensing device which is positioned at the downstream end of an extractor belt which forms the bottom of the apparatus, so as to dispense the colouring agent onto the surface of the layer of mix conveyed by said extractor belt towards the position where it falls freely onto said temporary moulding support.
The colouring or pigmenting agent used may be in solid form (dry powder) or liquid form and may be supplemented or replaced with coloured or reflective granules.
By means of this method it is possible to obtain slabs and articles which have a veined effect throughout their thickness.
However this method is also not without drawbacks.
Firstly, performing addition of the colouring agents before the vibrocompression step has the effect that the liquid colouring agent is diffused lightly within the mass of the mix.
This diffusion results in blurred veining which is not clear and well-defined like the veining present in natural stone.
Moreover, still with reference to the liquid colouring agent, cleaning of the plant is particularly complex since each nozzle must be disassembled and cleaned and each individual pipe supplying the colouring liquid to the nozzles must be cleaned.
The same procedure must also be performed in the case where it is required to change the veining effect to be performed on the slab, both in terms of different colouring and in terms of a different effect associated with the arrangement of the veining.
The use of the powdery colouring agent would result in a more pronounced veining, similar to that of natural stone, but considerable difficulties exist with regard to distribution of the powdery colouring agent, both in terms of the random nature of the distribution and in terms of suitable distribution of the colouring agent.
The object of the present invention is therefore to overcome the drawbacks of the prior art.